This project has been directed primarily at understanding cell- mediated immune cytotoxicity in humans. The long-range goals are: 1) to identify human cells capable of destroying foreign cells by cytotoxic, cell-mediated immune reactions; 2) to characterize factors which influence development of cellular immune effector cells; 3) to characterize mechanisms of foreign cell destruction by effector cells, and 4) to define changes occurring in the cellular immune deficiency disease, malignancies, transplanted organs, autoimmune states, and iatrogenic immune suppression.